the ideas of evolutionary change and natural selection were two extraordinary contributions of 19th-century science to culture and society. charles darwin formalized the first idea from some outstanding antecedents and entirely invented the second one, although he delayed the publication of both. some of darwin's own comments gave rise to the impression that he deferred publication because he remained summarizing information and making new observations while searching for an explanation of evolutionary change (i.e., the causal mechanism). this story might not fit the facts, however, since darwin appears to have conceived his theory very soon in his life, perhaps before 1840. apparently, darwin aspired to publish the theory only when it appeared unquestionable but when he wrote down his ideas in detail exposing its critical assumptions and deducing several "expected observations" he noted numerous drawbacks in both. fearful of the reactions of their colleagues, he delayed publishing the theory. darwin did not postpone publication because he was looking for the explanation of evolutionary change between 1840 and 1858; he already had the explanation and remained obsessively testing it. the process through which evolutionary theory was conceived highlights the key role of creativity in the development of human knowledge and, therefore, constitutes a valuable model to consider when teaching about "scientific discoveries".